The present invention relates in general to brake actuators of railway or similar type vehicles and, in particular, the invention relates to a pneumatic actuator.
Actuators which consist of a tubular housing equipped with a cylinder at one end in which slides, under the action of a fluid under pressure and against the action of an elastic retraction means, a piston with a hollow shaft connected thereto and which does not rotate in relation to the tubular housing and in which is axially connected a threaded rod to operate the braking means, in which the rod is also nonrotating with respect to the tubular housing are known. During the braking action of the threaded rod, a clutch-type, self-adjusting mechanism changes the relative axial position of the threaded rod and the hollow shaft, as the above-mentioned braking means wear down.
According to this application, the automatic self-adjusting device consists of an internally threaded stopping ring which screws on a threaded rod and has a frontal coupling part which fits the corresponding frontal coupling part of the hollow shaft to block the rotating of the stopping device, in relation to the hollow shaft, and elastic retraction means are provided to restore the engagement of these coupling parts, by the screwing of the retaining element in relation to the threaded rod, after an axial separation between these coupling parts.
In addition, between the tubular housing and the threaded rod is placed a friction ring which acts on the threaded rod and slides together with it in relation to the housing, during the operation of the actuator, for a predetermined stroke. Limit stops are placed on the housing to stop the friction ring at the end of such predetermined stroke and to allow for an axial sliding of the threaded rod in relation to the hollow shaft, in order to adjust for any wear of the braking means.
Therefore, in this known actuator the threaded rod will slide out of the hollow shaft every time the advancement of the hollow shaft is greater than the normal brake stroke defined by the limit stops.
This overtravel may be due to the normal wearing of the braking device and also to the elastic give of the transmission elements, which connect the actuator to the brake unit. These elements generally consist of two caliper arms, one connected to the actuator housing and the other to the free end of the threaded rod, and which have a pair of friction pads adapted to a wheel of the railway or similar type vehicle.
The action to adjust for the above-mentioned play and elastic give is generally negligible and not sufficient to effect the correct operation of the actuator. However, in some particular applications, the action of the self-adjusting device to take up the play due to such elastic give is undesirable and must be eliminated.